There are two types of links: absolute and relative.
Absolute links are simple. It’s an entire web address.
Relative links are based on the address you’re currently on.
Say I wanted to go to my themes page. We’re currently inside the "misc" folder, which themes isn't in, so a link like this…
To link back to a page outside of the folder, add a forward slash in front of the link.
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But if I wanted to go to another page that’s in the same folder, I'd be fine without the forward slash.
The forward slash indicates that we want to “reset” the website back to its beginning point, also known as the index. So rather than use “misc/” as the starting point, it will use "/".
Thus, if you want to link back to your index page, just do:
Final Notes: If you’re wondering why “index.html” is a website’s starting page, it’s because you can’t name a file nothing.
Additionally, a folder can have an “index.html” inside of it, and it will act as if it's named the folder name. So if you have a folder named “croutons” and have “index.html” in it, “/croutons” will redirect to that “index.html”.
Further Reading